My Secret Panda Express Beijing Beef is SO Easy

Ingredients

• 1 lb (450g) flank steak, thinly sliced against the grain
• 1/4 cup (30g) cornstarch
• 1/4 cup (30g) all-purpose flour
• 1 teaspoon baking powder
• 1/2 teaspoon salt
• 1/4 teaspoon black pepper
• 1 large egg, beaten
• Vegetable oil, for frying (at least 3 cups / 700 ml)
• 1/4 cup (60ml) soy sauce, low sodium
• 1/4 cup (60ml) rice vinegar
• 1/4 cup (50g) granulated sugar
• 2 tablespoons ketchup
• 1 tablespoon hoisin sauce
• 1 tablespoon water
• 1 teaspoon cornstarch
• 1/2 teaspoon ground ginger
• 1/4 teaspoon garlic powder
• 1/4 teaspoon red pepper flakes (optional, for heat)
• 1 green bell pepper, cut into 1-inch pieces
• 1/2 yellow onion, cut into 1-inch pieces